1. Field of the Invention
This invention relates to a rotary actuator assembly for a disk drive. More particularly, this invention relates to a rotary actuator assembly having a constrained layer damper attached to a flat actuator coil.
2. Description of the Prior Art and Related Information
A huge market exists for hard disk drives for mass-market host computer systems such as servers, desktop computers, and laptop computers. To be competitive in this market, a hard disk drive must be relatively inexpensive, and must accordingly embody a design that is adapted for low-cost mass production. In addition, it must provide substantial capacity, rapid access to data, and reliable performance. Numerous manufacturers compete in this huge market and collectively conduct substantial research and development, at great annual cost, to design and develop innovative hard disk drives to meet increasingly demanding customer requirements.
Each of numerous contemporary mass-market hard disk drive models provides relatively large capacity, often in excess of 40 gigabytes per drive. Nevertheless, there exists substantial competitive pressure to develop mass-market hard disk drives that have even higher capacities and that provide rapid access. Another requirement to be competitive in this market is that the hard disk drive must conform to a selected standard exterior size and shape often referred to as a “form factor.” Generally, capacity is desirably increased without increasing the form factor or the form factor is reduced without decreasing capacity.
Satisfying these competing constraints of low-cost, small size, high capacity, and rapid access requires innovation in each of numerous components and methods of assembly including methods of assembly of various components into certain subassemblies. Typically, the main assemblies of a hard disk drive are a head disk assembly and a printed circuit board assembly.
The head disk assembly includes an enclosure including a base and a cover, at least one disk having at least one recording surface, a spindle motor for causing each disk to rotate, and an actuator arrangement. The printed circuit board assembly includes circuitry for processing signals and controlling operations.
Actuator arrangements can be characterized as either linear or rotary; substantially every contemporary cost-competitive small form factor drive employs a rotary actuator arrangement.
The rotary actuator arrangement is a collection of elements of the head disk assembly; the collection typically includes certain prefabricated subassemblies and certain components that are incorporated into the head disk assembly. The prefabricated assemblies include a pivot bearing cartridge and, in some cases, a prefabricated head stack assembly which typically includes the pivot bearing cartridge installed in its bore. Other components of the rotary actuator arrangement are permanent magnets and an arrangement for supporting the magnets to produce a magnetic field for a voice coil motor. The prefabricated head stack assembly includes a coil portion having a coil support and a coil forming another part of the voice coil motor. The prefabricated head stack assembly also includes a rotary actuator assembly, which includes an actuator body having a bore through it, and a plurality of actuator arms projecting parallel to each other and perpendicular to the pivot axis of the bore. The prefabricated head stack assembly also includes head gimbal assemblies that are supported by the arms. Each head gimbal assembly includes a load beam and a head supported by the load beam.
The rotary actuator assembly has various natural modes of vibration. One such mode is referred to as a “butterfly” resonance mode (“butterfly mode”) or the first principal bending mode. During such a butterfly mode, the actuator arms and the coil support slightly flex or bend toward and away from each other in a plane orthogonal to the axis of rotation (“pivot axis”) and the heads move away from its position on the disk. This is due to those electromagnetic forces in a direction perpendicular to a longitudinal axis of the rotary actuator assembly produced by the current through the coil and the electromagnetic forces interaction with the magnetic fields of the permanent magnets. Thus, if the natural frequency of the butterfly mode is 5 kilo hertz and the applied current into the coil has a 5 kilo hertz component, then this will result in the potential for undesirable excitation of the butterfly mode. While a filter, such as a notch filter, may be used to remove the frequency component corresponding to the natural frequency of the butterfly mode, that may negatively impact the capability of the actuator servo control system by reducing its bandwidth.